Two-Stage Digital AGC for Stable Video Conferencing Audio
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Solution Overview
Problem
Video conferencing systems face challenges in maintaining a stable and consistent audio signal level, leading to unpredictable audio quality and unpleasant auditory experiences due to variations in speech levels.
Innovation Solution
A two-stage automatic gain control (AGC) module is implemented, which includes a long-term level estimator and a short-term level estimator, using voice activity detectors to filter noise and apply gain parameters to amplify the audio signal to a target level, ensuring consistent audio quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a single-stage AGC is used, then the device complexity is low, but the audio signal level stability is poor
Solution Approach 1:
The AGC module is divided into two distinct stages: a long-term level estimator that provides gradual gain adjustment for stability, and a short-term level estimator that provides immediate gain adjustment for rapid convergence. This segmentation allows each stage to specialize in different temporal aspects of gain control, resolving the contradiction between stability and complexity by distributing functionality across multiple components rather than using a single complex stage.
2Speed
If gain adjustment is applied rapidly, then the convergence speed is improved, but the audio quality and pleasantness deteriorate due to over-correction
Solution Approach 1:
The system dynamically switches between two gain adjustment modes based on operational state. During the unconverged state, the short-term estimator provides rapid gain adjustment for fast convergence. Once converged, the system transitions to using the long-term estimator for gradual, stable adjustments. This dynamic switching resolves the contradiction by adapting the adjustment speed to the current operational phase, preventing over-correction while maintaining fast initial convergence.
3Measurement precision
If noise filtering is applied, then the signal-to-noise ratio is improved, but the response time to speech changes increases
Solution Approach 1:
The system employs periodic action by using two different estimation time scales. The short-term level estimator operates with a small time constant to rapidly respond to speech changes, while the long-term level estimator operates with a large time constant to provide accurate noise-filtered baseline levels. By periodically switching between these two estimation modes based on convergence state, the system achieves both fast response and accurate noise filtering without compromising either aspect.
Data Source
AI summary
Disclosed are systems and methods for automatic control of gain in audio and video conferencing applications to maintain a predetermined and stable audio level. In one embodiment, a first stage applies a first stage gain based on a long-term estimate of signal level, while a second stage gain, based on a short-term estimate of signal level assists the first stage gain to achieve a target level. Some embodiments of long-term level estimation utilize statistical analysis of a buffer to validate or arrive at a more accurate long-term signal level estimate.